Cathode heater system for electron discharge device



Oct. 20, 1959 E. c. oKREss 2,909,701

CATHODE HEATER SYSTEM FOR ELECTRON DISCHARGE DEVICE Filed July s, 1955 2 sheets-sheet 1 sir, Ernsf C.Okress @www M ATTORNEY CATHODE HEATER SYSTEM FOR ELECTRON DISCHARGE DEVICE Filed July 6, 1955 E. C. OKRESS Oct. 20, 1959 2 Sheets-Sheet 2 CATHODE HEATER' SYSTEM FOR ELECTRON DISCHARGE DEVICE Ernest C. Okress, Elmira, N.Y;,A assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania t Application July 6, 1955,`.Serial No.,520,188 '5 Claims. (Cl. 313-278) This invention relates toelectron discharge devices and, more particularly, to a cathode heater assembly for an electron discharge device.

It is an object of this invention to provide an electron discharge device having an improved cathode heater system. v

Another object is to provide an electron discharge device having an improved cathode heater filament structure.

A further object is to provide an electron discharge device with an improved cathode heater which is compensated for variations in temperature.

An additional object is to provide an electron discharge device having a non-inductivev cathode heater system.

It is a different object to provide an improved cathode heater system having a -substantial thennal drop from thev cathode heater filament to the refractory insulators.

Still another object is to provide an improved cathode heater system suitable for use in a magnetron.

These and other objects ofthe invention will be apparent from the following description taken in accord` ance with the accompanying drawings, which form a part of this application, and in which:

Figure 1 is a top sectional view of a typical prior art magnetron in which type ofV electron discharge device my invention may be employed;

Fig. 2 is a sectional View of a cathode assembly embodying a rst form of my invention;

Fig. 3 is a cross-sectional view along line III--III of Fig. 2;

Fig. 4 is a cross-sectional view along line IV-IV of Fig. 2;

Fig. 5 is a sectional view of a cathode assembly embodying a second form of my invention;

Fig. 6 is across-sectional view along line VI-VI of Fig. 5; and

Fig. 7 is a cross-sectional View along line VII-VII of Fig. 5.

In Fig. 1 there Ais shown a magnetron 11 including a housing body or anode portion 13 and plates or vanes 15. The plates or vanes 15, in cooperation withthe anode portion 13, generally define triangular, trapezoidal or sector-shaped pockets .17, all of said pockets 17 being connected with a `central chamberor pocket 19 where a cathode 21 is positioned. The cathode 21 in the present embodiment is shown as enclosing a helical filament 23 made preferably of tungsten. An electron emitting housing 25 includes an oxide coating 27, such as -thorium oxide, on a cylindrical sleeve 29 which may be composed of a metal suchas molybdenum or tantalum. Also shown is the coaxial terminal or output lead 33.L Other coupling means than the coaxial terminal or output lead 33 may be used. v

The operation of a magnetron of this type is more fully described in the United States Patent No. 2,520,- 955, entitled Trapezoidal Cavity Magnetron, Okress et al., issued September 5, 1950, and assigned to the same assignee as this application.

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Fig. 2 is an embodiment of one form of my invention including a cathode 35 comprising a cylindricalv sleeve 37, which is coated with an electron emissive layer 39.

The cathode heater 40 includes heater ilament members 41 which are substantially straight and comparatively heavy, e.g., 0.120 inch diameter. The heater 40 is rigidly supported at one end yby the lament base assembly 43 and at the other end by the filament support assembly 45. The filament support assembly 45 is longitudinally movable on an axial pin member 47 which is attached to an axial pin support member 49. The lament support.

assembly 45 will move in either direction along the axis of the axial pin member 47, because of the relative expansion and contraction of the filament members 41 and the axial pin support member 49 due to temperature variations. The filament support assembly 45 and the filament base assembly 43 include filament support members 51 and 53 in physical contact with the filament mem? 7bers 41. Electrical insulator members 55 and 57 are in physical contact with the filament support members 51 and 53, respectively, 'but are not in such contact with the filament members 41. The filament support members 51 and 53 are made of a material with a high melting point, eg., tantalum. In this way, a substantial thermal drop from the filament members 41 to the electrical insulator members 55 and 57 is provided by means of the filament support members 51 and 53 and the safe operating temperature of the respective electrical insulator members S5 and 57 is not exceeded. A top housing member 59 encloses the top of the cathode assembly. The cathode 35 is supported by a bottom housing member 8l. The flange portions of the bottom housing member 81 are secured together by screw members 79 or other suitable fasteners. Heater filament member lead portions 87 are supported by lead support members 85.

In order to form a non-inductive lament system, an even number of filament members 41 are connected in series thereby reducing the creation of stray magnetic iields to a negligible amount. A non-inductive filament system is preferable because the associated magnetic field leakage due to high heater current would otherwise interfere with the operation of the electron .discharge device.

Fig. 3 is a View of Fig. 2 along line lII-III showing a cylindrical cathode sleeve 37, the heater filament members 41, the axial pin support member 49, the axial pin member 47, the filament support members 51, the top housing member 59, and a part of the filament support assembly 45.

Fig. 4 is a view of Fig. 2 along line IV-IV showing a cylindrical cathode sleeve 37, the heater filament member lead portions 87, the bottom housing member 81, the axial pin support member 49, the filament base assembly support member 83, the lead support members and screw members 79.

The elements of Figs. 2, 3 and 4 may be composed of, but are not limited to, the following materials: cylindrical sleeve 37, molybdenum or tantalum; electron emissive layer 39, thorium oxide; heater filament members 41, tungsten; filament support members 51 and 53, tantalum; electrical Ainsulator members 55 and 57, a refractory material such as aluminum oxide or beryllium oxide; axial pin member 47, tungsten; bottom housing member 81, molybdenum; filament base support member 83, molybdenum; the lead support members 85, molybdenum; axial,

and is rigidly supported by heater support members 7l at one end. The other end of the heater 67 is movable along its axis and is attached to and guide by an axial pin system 70. The helical filament member 69 longitudinally moves the axial pin member 72. The longitudinal motion of the helical filament member 69, due to changes in temperature, will move the axial pin support member 73 in either direction along the axis of the guide member 75. In this Way, no internal stress is caused in the helical filament member 69, because of thermal expansion or contraction, as would be the case if both ends of the helical filament member 69 were rigidly anchored. The guide member 75 is set in a top housing member 77, and the cathode 61 is supported by a bottom housing member 74. The flange portions of the bottom housing member 74 are secured together by screw members 76 or other suitable fasteners. Heater filament member lead portions 93 are supported by heater support members 71.

Fig. 6 is a view of Fig. 5 along line VI-VI showing the cylindrical sleeve 63, the helical filament member 69, the bottom housing member 74, the screw members 76 and the axial pin member 72,

Fig. 7 is a view of Fig. 5 along line VIl-VII showing the bottom housing member 74, screw member 76, filament member lead portions 93, heater support members 71, base member 91.

The elements of Figs. 5, 6 and 7 may be composed of, but are not limited to, the following materials: cylindrical metal sleeve 63, molybdenum; electron emissive layer 65, thorium oxide; helical filament member 69, tungsten; axial pin member 72, tungsten; axial pin support member 73, molybdenum; guide member 75, beryllium oxide; tcp housing member 77, molybdenum; bottom housing member 74, molybdenum; base member 91, tungsten; and heater support members 71, molybdenum.

The cathode in all embodiments shown should be of the refractory type in order to withstand the high temperature which may be too high for a non-refractory cathode. The straight filament type of embodiment of the present invention as pictured in Figs. 2, 3 and 4 has certain advantages over the helical filament type embodiment as shown in Figs. 5, 6 and 7, and over the helical filament type that was common in prior art. If tungsten, the preferred material, is used, difficulties are encountered in forming and shaping a large diameter wire. Even if the Wire does not break, it may be fragile after it is formed. Thermal expansion compensation, as in the helical structure disclosed in Fig. 5, and in the straight filament structure, as disclosed in Fig. 2 and the straight filament structure itself, as disclosed in Fig. 2, minimize this difficulty. It a thin helical filament were used, it would require continuous support by refractory insulators, which is not practical because, at the high filament temperatures necessary for operation, activation and degassing, there would be a reaction between the filament and the refractory insulator, thus gassing the device and destroying the filament. As disclosed previously relative to Fig. 2, a substantial thermal drop is provided between the filaments 41 and the refractory electrical insulators 55 and 57 by the filament support members 5l and 53, and, therefore, the safe operating temperature of the refractory electrical insulators 55 and 57 is not ex ceeded.

The same principles apply to the structure of Fig. wherein a substantial thermal drop occurs between helical filament member 69 and the guide member 75.

While the present invention has been shown in certain embodiments only, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modifications without departing from the spirit thereof.

I claim as my invention:

1. In an electron discharge device, the combination of a cathode assembly including -a cathode and a non-inductive internal cathode heater, said cathode heater having an axis and a first and a second end, said first end being rigidly supported `and said second end being slidably supported and being movable along said axis to compensate for changes in the axial length of said cathode heater due to temperature variations, said cathode heater being supported at said ends only, and electrical insulator means electrically insulating said second end from the rest of said `discharge device.

2. In an electron discharge device, the combination of a cathode `assembly including a. cathode and an internal cathode heater, said cathode heater having an axis and a first and a second end, said cathode heater including an even number of straight filament members, said first end of said cathode heater ybeing rigidly supported and said second end of Said cathode heater being movable along said axis to compensate for changes in axial length of said cathode heater due to temperature variations.

3. In an electron discharge device, the combination of a cathode assembly including a cylindrical cathode' and an internal cathode heater, said cathode heater having an axis and a iirst and a second end, said cathode heater including a plurality of cylindrically arranged straight filament members positioned co-axially relative to the axis of said cathode, said first end of said heaterbeing rigidly supported and said second end of said cathode heater being attached to a filament support member, an axial pin, said lament support member being movable along the axis on said axial pin.

4. In an electron discharge device, the combination of a cathode assembly including la cathode and a noninductive internal cathode heater, said cathode heater having an axis and a first and a second end, said cathode heater including a helical filament member, an axial pin system, said first end of said cathode heater being rigidly supported and said second end of said cathode heater being movable along said axis to compensate for changes in the axial llength of said cathode heater due to temperature variations, said second end of said cathode heater being slidably attached to and guided by said axial pin system, said cathode heater being supported -at said ends only, and electrical insulator means electrically insulating said second end `from the rest of `said discharge device.

5 In an electron discharge device, `a cathode assembly including a cathode and a non-inductive internal cathode heater member, said cathode heater member having an axis and a first and a second end, said first end being rigidly supported and electrically connected to a source of electrical energy, said second end being slidably supported and being movable along said axis to compensate for changes in the axial length of said cathode heater member due to temperature variations, said cathode heater being supported at said ends only, an electrical insulator means electrically insulating said second end from the rest of said discharge device, said electrical insulator means being at least partially thermally insulated from said second end of said cathode heater.

References Cited in the tile of this patent UNITED STATES PATENTS 1,774,698 Braselton Sept. 2, 1930 1,989,819 Parrott Feb. 5, 1935 2,404,363 Chevigny July 23, 1946 2,466,922 Wax Apr. 12, 1949 

